Switching Frequency Up To 1 MHz Allows Smaller LLC ICs

Switching Frequency Up To 1 MHz Allows Smaller LLC ICs

San Jose, California: Power Integrations has launched a family of high-voltage LLC power-supply ICs that incorporate the controller, high-side and low-side drivers, and both MOSFETs in a single package. The HiperLCS devices have two modes of use (see the figure).

For high-efficiency design, a variable frequency controller provides zero voltage switching, eliminating switching losses and enabling designs with efficiency greater than 97% at nominal 66-kHz switching frequency.

If cost and size are the determining design criteria, then high switching frequency is preferred. In this case, efficiency still remains high—for example, 96% at 250 kHz, the frequency where maximum power is achieved.

Peter Rogerson, director of marketing communications and automated channel sales for Power Integrations, explained that previously, an LLC circuit would be implemented with discretes, which had to use lower switching frequencies.

“If you buy discrete MOSFETs from multiple suppliers, they may be slightly different quality, and if they switch at even slightly different times, you get ‘shoot through,’” he said, explaining that shoot through is catastrophic for the system.

“People usually run lower frequencies in this situation to avoid shoot through. But because we use our own MOSFETs in our own packaging, we can be sure of the quality and can therefore run at higher frequencies,” Rogerson explained.  

“Higher switching frequency means you need smaller magnetics and fewer capacitors, which means lower cost and smaller footprint,” he added.

The MOSFET’s accurate switching allows a high peak switching frequency of 1 MHz, so low-cost surface-mount device (SMD) ceramic capacitors can be used in the output loop instead of their bulky, unreliable electrolytic counterparts. In fact, the company says that HiperLCS can eliminate up to 30 discrete components from comparable LLC designs.

Power Integrations
www.powerint.com

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